An animal rights group believes shocking footage showing squalid and cruel conditions at a Christchurch pig farm is ''just the tip of the iceberg''.

The footage, filmed earlier this year, showed severe overcrowding, with a sow in a farrowing crate so small that her newborn piglets were squashed to death. Other piglets lay dying next to their helpless mother while other animals had infected eyes and obvious sores.

It also showed a dead pig that had been left to rot among living pigs and dozens of rats running over the animals.

The pork industry is now under fire after the TVNZ investigation.

Animal right group SAFE says the Government has failed these animals and is calling for a ban on farrowing crates.

SAFE's head of campaigns, Mandy Carter, said activists from Farmwatch visited the farm last year and filmed the animals in squalid, cruel conditions. The footage was referred to SAFE, who laid a complaint with the Ministry for Primary Industries (MPI).

Carter said significant non-compliance with the pig welfare code was found by MPI inspectors, and a number of pigs were in such bad shape they had to be killed immediately. A few months later MPI declared that improvements had been made and the farm now complied with the code.

MPI promised to undertake regular monitoring to ensure the ongoing welfare of the animals, Carter said.

''In April this year, the activists decided to visit the farm again and what they found was even worse.''

The condition of the animals was ''disgusting'', she said, and many sows and piglets were suffering.

After a 2009 campaign, led by SAFE and featuring comedian and ex-pork industry spokesperson Mike King, the Government undertook action to phase out sow crates by 2016.

''This Christchurch pig farm is really very bad, but the pig industry as a whole is not good,'' Carter said.

In the last couple of years SAFE had received footage from about 12 farms across the country, revealing similar levels of cruelty.

Carter said the footage of the Christchurch farm was ''unfortunately just the tip of the iceberg'', and consumers needed to know they could not trust New Zealand's pork industry.

She said the industry-led rating scheme called Pig Care had downgraded the farm's rating from green to amber after complaints, but it had since been changed back to green.

The Green Party is calling for an independent commissioner for animal welfare after discovering the "horrendous conditions" on the farm.

Animal welfare spokeswoman Mojo Mathers said pigs were still living in "disgusting and squalid" conditions on the farm, despite MPI saying it was compliant last year.

The ministry was failing at its job because it was putting economic interests ahead of animal welfare.

"We don't believe MPI is the right body to be monitoring animal welfare on intensive factory farms because they have a conflict of interest between promoting intensive farming and ensuring decent animal welfare," Mathers said.

"There is a strong need to safeguard the welfare of animals. This is not only essential if we are to maintain New Zealand's international reputation but is necessary to protect the viability of farmers who do put animal welfare first."

Farmwatch spokesman John Darroch said MPI had failed to protect these animals and had given the farm a clean bill of health after last year's investigation.

''We are disappointed that a year later the pigs are living in the same horrendous conditions,'' Darroch said.

"It is ridiculous for [MPI Minister] Nathan Guy to suggest that we should trust the ministry to manage this farm when they have clearly failed to take any real action until now.''

He said the reason the issue had not been addressed was because ''this is no rogue farm''.

''These are types of conditions which our organisation has found right around the country.''